R&D: Nanoscale Doping and Its Impact on Ferroelectric and Piezoelectric Properties of Hf0.5Zr0.5O2

Nanomaterials has published an article written by Anastasia Chouprik^, Roman Kirtaev, Evgeny Korostylev, Vitalii Mikheev, Maxim Spiridonov, and Dmitrii Negrov, Moscow Institute of Physics and Technology, 9 Institutskii Lane, Dolgoprudny 141700, Russia.

Abstract: “Ferroelectric hafnium oxide thin films – the most promising materials in microelectronics’ non-volatile memory—exhibit both unconventional ferroelectricity and unconventional piezoelectricity. Their exact origin remains controversial, and the relationship between ferroelectric and piezoelectric properties remains unclear. We introduce a new method to investigate this issue, which consists in a local controlled modification of the ferroelectric and piezoelectric properties within a single Hf_0.5Zr_0.5O₂ capacitor device through local doping and a further comparative nanoscopic analysis of the modified regions. By comparing the ferroelectric properties of Ga-doped Hf_0.5Zr_0.5O₂ thin films with the results of piezoresponse force microscopy and their simulation, as well as with the results of in situ synchrotron X-ray microdiffractometry, we demonstrate that, depending on the doping concentration, ferroelectric Hf_0.5Zr_0.5O₂ has either a negative or a positive longitudinal piezoelectric coefficient, and its maximal value is −0.3 pm/V. This is several hundreds or thousands of times less than those of classical ferroelectrics. These changes in piezoelectric properties are accompanied by either improved or decreased remnant polarization, as well as partial or complete domain switching. We conclude that various ferroelectric and piezoelectric properties, and the relationships between them, can be designed for Hf_0.5Zr_0.5O₂ via oxygen vacancies and mechanical-strain engineering, e.g., by doping ferroelectric films.“